1. Field
The embodiments relate to an optical sensor biosignal measurement apparatus and a method of controlling an optical sensor of the apparatus, and more particularly, to an optical sensor biosignal measurement apparatus which can appropriately adjust an optical transmission area of a photo detector of an optical sensor according to the strength of light detected by the photo detector, and thereby can reduce noise caused by external environments, such as interfering light, etc., and a method of controlling an optical sensor of the apparatus.
2. Description of the Related Art
As used in the present specification, the term “Ubiquitous” is an information communication environment where a user can be free to access networks at any place without being conscious of the surrounding networks or computers. If Ubiquitous is commercialized, anyone can readily use information technology not only at home or in a car, but also even on a mountaintop. Also, the commercialization of Ubiquitous may expand the information technology industry or the scope corresponding thereto by increasing the number of computer users who are connected to networks. Because of the advantage that users can access networks without restriction to time and place, not to mention its portability and convenience, countries worldwide are expanding development and competing in Ubiquitous-related technology now.
Ubiquitous-related technology may be applied to myriad fields in human life. In particular, Ubiquitous-HealthCare (hereinafter, U-HealthCare) has recently been in the spotlight as a notable technology area due to the “well-being” boom. U-HealthCare is Ubiquitous technology which enables anyone to readily receive medical services at any time and at any place by installing medical service-related chips or sensors in places within the user's living space. With U-HealthCare, various types of medical attention, such as physical examinations, disease management, emergency care, consultation with a doctor, etc., which currently are only performed in hospitals, may be naturally integrated into our daily lives, and thus may be accomplished without going to a hospital.
For example, a diabetic may wear a belt having a blood-sugar management system for blood-sugar management. A blood-sugar sensor attached to the belt may check the blood-sugar of the diabetic upon a specified occasion, and may calculate the amount of required insulin corresponding thereto. When the blood-sugar of the diabetic becomes drastically low or high, the belt may provide the blood-sugar information to his/her attending physician using a wireless network, and the attending physician who has received the blood-sugar information may write out an optimal prescription or take an optimal action for the medical emergency.
As an example of U-HealthCare, a portable biosignal measurement device to measure the user's biosignal using an optical sensor is being widely utilized. The user may carry the portable biosignal measurement device at all times and measure various types of biosignals, and thereby may prepare for an emergency situation. Accordingly, the portable biosignal measurement device may be regarded as a device capable of showing advantages of U-HealthCare.
The portable biosignal measurement apparatus includes a photoplethysmography (PPG) measurement device. A PPG includes information about a level of peripheral vasoconstriction, and increase and decrease in a cardiac output. Therefore, a physiological status associated with an arterial tube may be understood using the PPG measurement device. Also, the PPG measurement device may be generally utilized as an auxiliary diagnostic device for a particular disease.
Generally, a PPG signal may be measured from a user's finger, earlobe, etc. Specifically, a detector may detect the user's PPG signal by detecting light, passing through the finger, earlobe, etc., from a light source. However, when a PPG signal is weak, for example, a PPG signal detected from the earlobe, etc., a normal PPG signal may not be detected due to interference noise of disturbance light or motion.
When a measurement device measures a PPG signal from a body portion corresponding to a weak signal source, such as the earlobe, etc., a level of the PPG signal may be less than noise of the measurement device or the interference noise of the disturbance light or the motion. Therefore, although the weak PPG signal is amplified, the system noise is also amplified and thus a desired PPG signal may not be accurately detected.
As described above, the quantity of incidence light is one of the most important elements to determine a signal-to-noise ratio (SNR) when measuring a PPG signal using light. A conventional PPG measurement apparatus uses a method of initially adjusting the quantity of light in an initial state of measurement, that is, automatically selecting the quantity of light so that a PPG signal may be generated within an observance range, and thereby fixing the quantity of light.
However, when the disturbance light exists, it may be difficult to acquire a PPG signal within the observance range due to the disturbance light even though the quantity of light from a luminous element is adjusted. Particularly, when measuring a PPG signal while doing an outdoor activity, it may be more difficult to accurately measure a PPG signal due to various types of disturbance light effect, such as an external illumination, sunlight, a shadow, etc.
Accordingly, there is a need for an optical sensor biosignal measurement apparatus which can reduce the effect of disturbance light and thereby more accurately measure a biosignal when measuring the biosignal using an optical sensor.